This invention relates to the field of spiral-type hollow fiber membrane fabric-containing cartridges and modules for separations and other phase contact applications. In particular, this invention relates to improved cartridges and modules containing integral turbulence promoters. The teachings of this invention can, if desired, be used in conjunction with the subject matter of applicant's copending U.S. patent application entitled, "Spiral-Wound Hollow Fiber Membrane Fabric Cartridges and Modules Having Flow-Directing Baffles", filed concurrently herewith, which is hereby incorporated by reference.
There is a great deal of prior art relating to the structure, fabrication and use of spiral-type hollow fiber-containing cartridges. Among the early disclosures of such devices are Mahon U.S. Pat. No. 3,228,877 and McLain U.S. Pat. No. 3,422,008, both of which are incorporated herein by reference. In general, a bundle of hollow fibers is positioned around and parallel to the longitudinal axis of a rod-shaped core (which may be a hollow mandrel and may or may not be removed after the bundle is fabricated), the ends of the hollow fiber bundle are potted in tube sheets to form a cartridge, and the cartridge is fitted into a pressure housing suitably ported to facilitate feed, permeate and concentrate fluid flows, constituting a complete module.
More recently, the art has improved such cartridges and modules by forming the hollow fibers into a fabric-like web in which the hollow fibers, substantially parallel to the core axis, are held in place relative to each other by transverse filaments which may or may not also be hollow fibers.
Despite these developments, the challenge to optimize the operability, efficiency and durability of these hollow fiber-and hollow fiber-fabric-containing cartridges and modules has continued. The flow of fluids (both liquid and gaseous) through the bundle can present further problems for the operator, including channeling, growth of boundary layers and other inefficiencies in fluid/membrane contact (which may prevent effective mass transfer). Hence, some relatively recent developments in the art suggest the interposition of a turbulence-promoting web among loose hollow fibers or between layers of a hollow fiber fabric.
The Baurmeister U.S. Pat. No. 4,940,617 relates to a hollow fiber fabric-containing module having at least two plies of hollow fibers held in place by transverse fibers, disposed so that the hollow fibers of adjacent plies cross each other consistent with a prescribed formula including a numerical range for the crossing angles. Baurmeister discloses that to even out the flow of a fluid around the hollow fibers of the hollow fiber wound body, a fluid-permeable, more or less stiff or elastic fabric can be disposed between at least one portion of the hollow fiber plies of the hollow fiber wound body. The patent also refers to the channeling problem, and the desirability of radial flow (transverse to the hollow fibers). Further, Baurmeister makes passing reference to a hollow fiber mat with transverse fibers or tapes on only one side. Nowhere, however, does Baurmeister disclose or suggest the integration of a single-layer hollow fiber fabric and a co-extensive turbulence-promoting web on one side of the hollow fiber fabric, into an intermittently-bonded unitary material.
The McGinnis U.S. Pat. No. 3,690,465 relates to the broad concept of interposing a foraminous material between hollow fibers in a separatory unit. The stated purpose is to prevent hollow fiber movement and nesting. In one embodiment, the hollow fibers are placed on the foraminous material, the latter preferably being a web. The hollow fibers are preferably laid down more than one hollow fiber thick. In another embodiment, a hollow fiber is wound transversely and continuously around both sides of an advancing foraminous web, and the web and associated fiber is then assembled into a unit. In both types of such assemblies, each layer of hollow fibers will be adjacent to at least one additional layer of hollow fibers. As a result, there will be a significant amount of hollow fiber/hollow fiber direct contact, and a corresponding decrease in hollow fiber--shell side fluid contact. Moreover, there is no disclosure or suggestion in McGinnis to employ an integral hollow fiber array: loose hollow fibers or a continuous hollow fiber, are contemplated. There is no suggestion to intermittently bond the hollow fibers to the foraminous material across the full length of the fibers. Finally, there is no reference to the need for turbulence promotion. See also, Cope U.S. Pat. No. 3,801,401, which contains similar teachings.
The Smoot U.S. Pat. No. 4,689,255 relates to separatory units made from glass hollow fibers. The hollow fibers are collected in strands and the strands into rovings. The rovings are lined up parallel to each other in multiple layers on a permeable sheet, and another permeable sheet is laid on top (to dissipate fluid flow forces entering the mat when it is wrapped around a fluid distributor in a cartridge). The hollow fibers are bonded to the permeable sheet by strips or ribbons of adhesive. In this device, there is no disclosure or suggestion of using a hollow fiber fabric--instead, rovings are employed. The rovings are bonded only at their ends by strips/ribbons of adhesive.
Published P.C.T. application W083/00098 discloses a process for making an assembly of hollow fibers on one side of a foraminous support, which can then be wound into a spiral cartridge. The hollow fibers are sealed onto the support only at the ends. The hollow fibers are not in an integral array: they are laid down individually and sealed to the ends.
The Barer U.S. Pat. No. 4,460,641 relates to chemical-protective clothing comprising a hollow fiber fabric formed e.g., by weaving or knitting, and notes that composite fabrics can be used. A composite can be made by adhering hollow fiber fabric conventionally to various backing materials such as natural/synthetic cloths, fabrics, and permeable polymer films. This patent makes no reference to cartridges and modules for carrying out separations and other phase contact operations, nor to the problems attendant their conventional designs.
The Sekino U.S. Pat. No. 4,781,834 relates to a hollow fiber-containing device intended to overcome bundle flow stagnation and channeling. According to Sekino, the solution is to provide holes in the central core placed (only) at one end of the bundle, and an opening in a perimeter wrap (allowing retentate exit) placed at the other end: forcing radial flow. Optionally, gauze-like cloths can be put in the bundle near both ends, to improve radial distribution. These cloths are not continuous throughout the bundle length, and are not between each hollow fiber layer.
The Clark U.S. Pat. No. 4,080,296 relates to a hollow fiber permeator having a radial tubesheet at an intermediate position on the core. Clark notes in passing, that the fiber bundle may include means, such as fabric wraps, for constraining the bundle and/or improving the uniformity of feed fluid distribution between the fibers that form it. There is no explanation in the patent of where such wraps would be placed or how they would be constructed.
The Shah U.S. Pat. No. 4,707,268, relates to a microfilter comprising a hollow fiber bundle potted at both ends; the hollow fibers can be separated by radial ribs parallel to the core axis. Shah notes in passing that the hollow fibers can be contained in a screen matrix or fabric which is then wound around the core. It is unclear from this disclosure whether the hollow fibers themselves constitute the "fabric" or are somehow (unexplained) contained in a fabric.
The Krueger U.S. Pat. No. 4,666,469 discloses a hollow fiber membrane device having an inner wrap: a thin material located at 25% or less of the device radius away from the core. The wrap material surrounds and constrains inner fibers assembled about feed flow distribution means; the lumens of the constrained fibers are preferably sealed. The wrap may be discontinuous; it extends cartridge life. There is no disclosure of a hollow fiber fabric in this patent.
Despite these many efforts in hollow fiber cartridge design, the need for improvement continues.
It is therefore an object of this invention to provide improved spiral-type hollow fiber membrane fabric-containing cartridges containing a hollow fiber fabric-like array integrally-bonded to a turbulence-promoting, co-extensive web, for separations and other phase contact applications.
It is another object of this invention to provide such cartridges incorporated in modules for carrying out separations and other phase contact applications.
Further objects will be set forth in the discussion below.